JP4777666B2 - Carbon membrane and method for separating water and organic solvent using carbon membrane - Google Patents

Description

  The present invention relates to a carbon membrane used for separating water and an organic solvent from a liquid mixture containing water and an organic solvent by utilizing pores of the carbon material.

  In recent years, ethanol production using biomass technology has attracted attention from the viewpoint of environmental protection and effective use of waste materials. Conventionally, as a method for recovering ethanol produced by such biomass technology, a method using selective permeability of a zeolite membrane has been performed. This is to separate ethanol and water by bringing a liquid mixture containing water and ethanol obtained from woody biomass into contact with the zeolite membrane and selectively allowing only water to permeate.

  By the way, in a liquid mixture containing water and ethanol obtained from woody biomass, in addition to water and ethanol, organic acids such as acetic acid are also mixed. There is concern about the decrease in separation performance and early deterioration due to acid.

In addition, research has been conducted in which a carbon membrane, which has been mainly used for separation of a specific component from a gas mixture, is used for separation of water and an organic solvent such as ethanol (for example, non-patent literature). 1)), in order to obtain a carbon membrane having an excellent separation performance which can be used as a substitute for a conventional zeolite membrane, it is actually necessary to study further.
Hidetoshi Kita, Koji Nanbu, Hiroshi Maeda, Ken-ichi Okamoto, ACS Symposium Series (American Chemical Society), 2004, p.203-217, Gas Separation and Pervaporation through Microporous Carbon Membranes Derived from Phenolic Resin

  The present invention has been made in view of such conventional circumstances, and the object of the present invention is a carbon membrane excellent in separation performance and acid resistance between water and an organic solvent such as ethanol, and the carbon membrane. And to provide a separation method capable of stably separating water and an organic solvent such as ethanol over a long period of time even in an acidic environment.

According to the present invention, a carbon film precursor composed of a resin layer formed on the surface of a porous substrate is carbonized by pyrolysis in a temperature range of 400 to 1000 ° C. in an oxygen inert atmosphere. A carbon film that is immersed in an acetic acid aqueous solution or an aqueous citric acid solution at least once after the carbonization for 1 to 24 hours, and is subjected to a treatment for adsorbing acetic acid molecules or citric acid molecules to pore walls, Provided.

  According to the present invention, a liquid mixture containing water and an organic solvent is brought into contact with one side of the carbon membrane, and water is selectively permeated to the opposite side of the carbon membrane, whereby the water and the A method for separating water from an organic solvent using a carbon membrane, which separates the organic solvent, is provided.

In addition to being excellent in acid resistance, the carbon membrane of the present invention is immersed at least once in an acetic acid aqueous solution or citric acid aqueous solution for 1 to 24 hours, and is subjected to a treatment for adsorbing acetic acid molecules or citric acid molecules to the pore walls. As a result, the separation performance between water and an organic solvent such as ethanol is improved, and excellent separation performance comparable to that of conventionally used zeolite membranes is exhibited. Further, in the separation method of the present invention, by using the carbon membrane having excellent separation performance and acid resistance as described above, even in an acidic environment, an organic solvent such as water and ethanol is used. Can be stably performed over a long period of time with high efficiency.

As described above, the carbon film of the present invention is obtained by thermally decomposing a carbon film precursor formed of a resin layer formed on the surface of a porous substrate in a temperature range of 400 to 1000 ° C. in an oxygen inert atmosphere. The carbon film obtained by carbonization is immersed in an acetic acid aqueous solution or an aqueous citric acid solution for 1 to 24 hours at least once after the carbonization, and is subjected to a treatment for adsorbing acetic acid molecules or citric acid molecules to the pore walls. This is the main feature.

In order to recover ethanol from a liquid mixture containing water and ethanol obtained from biomass, the zeolite membrane that has been used for the separation of water and ethanol has low acid resistance, so that acetic acid present in the liquid mixture is present. There are concerns about damage due to organic acids such as and early performance degradation. On the other hand, carbon membranes have better acid resistance than zeolite membranes and exhibit stable separation performance over a long period of time. Furthermore, as shown in the examples described later, the carbon film is not only excellent in acid resistance, but is immersed at least once in an acetic acid aqueous solution or citric acid aqueous solution for 1 to 24 hours to finely bind acetic acid molecules or citric acid molecules. It has been confirmed by the study of the present inventor that the separation performance between water and an organic solvent such as ethanol is improved when a treatment for adsorbing to the pore wall is performed. Therefore, the carbon membrane of the present invention has high acid resistance and at the same time exhibits excellent separation performance in separating water from an organic solvent.

  Moreover, the separation method of the present invention is such that a liquid mixture containing water and an organic solvent is brought into contact with one side of the carbon membrane of the present invention, and water is selectively permeated to the opposite side of the carbon membrane. It is characterized by separating water and an organic solvent.

  As described above, the carbon membrane of the present invention has high acid resistance and at the same time has excellent separation performance between water and organic solvent, so that separation of water and organic solvent can be performed even in an acidic environment. It can be carried out stably with high efficiency over a long period of time, and can be suitably used for separation of water and an organic solvent such as ethanol in the biomass field as described above.

The carbon film of the present invention is not particularly limited with respect to its precursor, that is, the resin layer before being carbonized by thermal decomposition, but as a preferred one, the repeating unit is represented by the following general formula (1). Polyimide resin (where X is an aliphatic group having 2 to 27 carbon atoms, a cyclic aliphatic group, a monocyclic aromatic group, a condensed polycyclic aromatic group, and an aromatic group directly or crosslinked) 4 represents a tetravalent group selected from the group consisting of non-condensed polycyclic aromatic groups connected to each other by a member, n represents an integer of 5 to 10,000, and Y is represented by the following general formula (2). In the general formula (2), at least one of the phenylene groups forming the main chain skeleton is an m-phenylene group, and Z is a direct bond, —O—, —CO—, —S—, —SO ₂ —. _{, -CH 2 -, - C (} CH 3) 2 - or -C (CF _{3) 2} - indicates, m is It indicates to 3 integers, also, R _1-4 and R _'1-4 may, -H, -F, -Cl, -Br , -I, -CN, -CH 3, -CF 3, -OCH 3 , Phenyl group, 4-phenylphenyl group, phenoxy group or 4-phenylphenoxy group, and R _1-4 and R ′ _1-4 may be the same or different, and only a part thereof A polyamic acid represented by the following general formula (3), which is a precursor of the same (which may be the same) (wherein X and Y represent the same groups as described above) is applied to the surface of the porous substrate. And those formed by heating and drying.

Among the polyimide resins represented by the general formula (1), examples of those that can be suitably used in the present invention include those represented by the following structural formula (4) or (5).

The polyamic acid and the polyimide resin may be produced by any method. The polyamic acid and the polyimide resin are diamines represented by the following general formula (6) (in the general formula (6), at least one of an amino group and Z and / or a phenylene group that binds Z and Z is m. - phenylene group, Z is directly connected, -O -, - CO -, - S -, - SO 2 -, - CH 2 -, - C (CH 3) 2 - or -C (CF _{3) 2} - and M represents an integer of 1 to 3, and R _1-4 and R ′ _1-4 represent —H, —F, —Cl, —Br, —I, —CN, —CH ₃ , —CF. ₃ , —OCH ₃ , phenyl group, 4-phenylphenyl group, phenoxy group or 4-phenylphenoxy group, and R _1-4 and R ′ _1-4 may be the same or different, And only a part thereof may be the same) and tetracarboxylic dianhydrides represented by the following general formula (7) (wherein Is an aliphatic group having 2 to 27 carbon atoms, a cycloaliphatic group, a monocyclic aromatic group, a condensed polycyclic aromatic group, or a non-condensed polycycle in which aromatic groups are connected to each other directly or by a bridging member A tetravalent group selected from the group consisting of a formula aromatic group) can be used as a monomer.

  As for the diamine used for manufacture of the said polyamic acid and a polyimide resin, the at least 1 sort (s) of compound represented by General formula (6) is mentioned. Specific examples include, but are not limited to, for example, in the diamines of general formula (6) where m = 1, 3,3′-dichlorobenzidine, 3,3′-dimethylbenzidine, 3,3′- Dimethoxybenzidine, 3,3′-diaminodiphenyl ether, 3,3′-diamino-5,5′-ditrifluoromethyldiphenyl ether, 3,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl sulfide, 3,4′- Diaminodiphenyl sulfide, 3,3′-diaminodiphenylsulfone, 3,4′-diaminodiphenylsulfone, 3,3′-diaminobenzophenone, 3,3′-diamino-4,4′-dichlorobenzophenone, 3,3′- Diamino-4,4′-dimethoxybenzophenone, 3,3′-diamino-4-phenoxyben Phenone, 3,3′-diamino-4,4′-diphenoxybenzophenone, 3,3′-diamino-4- (4-phenyl) phenoxybenzophenone, 3,3′-diamino-4,4′-di (4 -Phenylphenoxy) benzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2,2-bis (3-aminophenyl) propane, 2,2-bis (4 -Aminophenyl) propane, 2,2-bis (3-aminophenyl) -1,1,1,3,3,3-hexafluoropropane and the like, and diamines of m = 2 in the general formula (6) 1,3-bis (3-aminophenyl) benzene, 1,3-bis (4-aminophenyl) benzene, 1,4-bis (3-aminophenyl) benzene Zen, 1,3-bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (3-aminophenoxy) benzene, 1,3-bis (3-amino) Benzoyl) benzene, 1,3-bis (4-aminobenzoyl) benzene, 1,4-bis (3-aminobenzoyl) benzene, 1,3-bis (3-aminophenyl sulfide) benzene, 1,3-bis ( 4-aminophenylsulfide) benzene, 1,4-bis (3-aminophenylsulfide) benzene, 1,3-bis (3-aminophenylsulfone) benzene, 1,3-bis (4-aminophenylsulfone) benzene, 1,4-bis (3-aminophenylsulfone) benzene, 1,3-bis (3-aminobenzyl) benzene, 1,3-bis (4-amino) Nobenzyl) benzene, 1,4-bis (3-aminobenzyl) benzene, 1,3-bis (3-amino-α, α-dimethylbenzyl) benzene, 1,3-bis (4-amino-α, α- Dimethylbenzyl) benzene, 1,4-bis (3-amino-α, α-dimethylbenzyl) benzene, 1,3-bis (3-aminophenoxy) -4-trifluoromethylbenzene, 1,3-bis (3 -Aminophenoxy) -5-trifluoromethylbenzene, 1,3-bis (4-aminophenoxy) -4-trifluoromethylbenzene, 1,3-bis (4-aminophenoxy) -5-trifluoromethylbenzene, 1,4-bis (3-aminophenoxy) -3-trifluoromethylbenzene, 1,3-bis (3-amino-5-trifluoromethylphenoxy) benzene 1,3-bis (3-amino-4-trifluoromethylphenoxy) benzene, 1,3-bis (4-amino-2-trifluoromethylphenoxy) benzene, 1,3-bis (4-amino-3- Trifluoromethylphenoxy) benzene, 1,4-bis (3-amino-5-trifluoromethylphenoxy) benzene, 1,4-bis (3-amino-4-trifluoromethylphenoxy) benzene, 1,3-bis (3-Amino-5-trifluoromethylphenoxy) -4-trifluoromethylbenzene, 1,3-bis (3-amino-5-trifluoromethylphenoxy) -5-trifluoromethylbenzene, 1,3-bis (3-Amino-4-trifluoromethylphenoxy) -4-trifluoromethylbenzene, 1,3-bis (3-amino-4-to Fluoromethylphenoxy) -5-trifluoromethylbenzene, 1,3-[(3-amino) -α, α-bis (trifluoromethyl) benzyl] benzene, 1,3-[(4-amino) -α, α-bis (trifluoromethyl) benzyl] benzene, 1,4-[(3-amino) -α, α-bis (trifluoromethyl) benzyl] benzene, 1,3-bis (3-amino-4-fluoro) Benzoyl) benzene, 1,3-bis (3-amino-4-phenoxybenzoyl) benzene, 1,3-bis [3-amino-4- (4-phenylphenoxy) benzoyl] benzene, 2,6-bis (3 -Aminophenoxy) benzonitrile, 1,3-bis (4-aminophenoxy) -2-phenylbenzene, and the like, and further in the case of diamines having m = 3 in the general formula (6), 4 , 4′-bis (3-aminophenoxy) biphenyl, 3,3′-bis (4-aminophenoxy) biphenyl, 3,3′-bis (3-aminophenoxy) biphenyl, bis [4- (3-aminophenoxy) ) Phenyl] ether, bis [3- (4-aminophenoxy) phenyl] ether, bis [3- (3-aminophenoxy) phenyl] ether, bis [4- (3-aminophenoxy) phenyl] ketone, bis [3 -(4-aminophenoxy) phenyl] ketone, bis [3- (3-aminophenoxy) phenyl] ketone, bis [4- (3-aminophenoxy) phenyl] sulfide, bis [3- (4-aminophenoxy) phenyl ] Sulfide, bis [3- (3-aminophenoxy) phenyl] sulfide, bis [4- (3-aminophenoxy) Phenyl] sulfone, bis [3- (4-aminophenoxy) phenyl] sulfone, bis [3- (3-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] methane, bis [3- (4-aminophenoxy) phenyl] methane, bis [3- (3-aminophenoxy) phenyl] methane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [3- (4-Aminophenoxy) phenyl] propane, 2,2-bis [3- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] -1,1,1 , 3,3,3-hexafluoropropane, 2,2-bis [3- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoro Propane, 2,2-bis [3- (3-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, and the like. These diamines can be used alone or as a mixture as required.

下式（９）で表される縮合多環式芳香族基、

及び下式（１０）で表される芳香族基が直接又は架橋員により相互に連結された非縮合多環式芳香族基からなる群より選ばれた４価の基であるテトラカルボン酸二無水物が使用される。

（式中、Ａは直接結合、−ＣＯ−、−Ｏ−、−Ｓ−、−ＳＯ₂−、−ＣＨ₂−、−Ｃ（ＣＨ₃）₂−、−Ｃ（ＣＦ₃）₂−、又は下式（１１）を示す）

（ここで、Ｂは直接結合、−ＣＯ−、−Ｏ−、−Ｓ−、−ＳＯ₂−、−ＣＨ₂−、−Ｃ（ＣＨ₃）₂−、−Ｃ（ＣＦ₃）₂−を示す） Examples of the tetracarboxylic dianhydrides used for producing the polyamic acid and the polyimide resin include at least one compound represented by the general formula (7). Specifically, in the general formula (7), X is an aliphatic group having 2 to 10 carbon atoms, a cyclic aliphatic group having 4 to 10 carbon atoms,
A monocyclic aromatic group represented by the following formula (8):

A condensed polycyclic aromatic group represented by the following formula (9):

And tetracarboxylic dianhydride, which is a tetravalent group selected from the group consisting of non-condensed polycyclic aromatic groups in which the aromatic group represented by the following formula (10) is directly or mutually linked by a bridging member Things are used.

Wherein A is a direct bond, —CO—, —O—, —S—, —SO ₂ —, —CH ₂ —, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —, or (Shows the following formula (11))

(Here, B represents a direct bond, —CO—, —O—, —S—, —SO ₂ —, —CH ₂ —, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —). )

  Examples of tetracarboxylic dianhydrides represented by the general formula (7) include, but are not limited to, for example, ethylene tetracarboxylic dianhydride, butane tetracarboxylic dianhydride, cyclobutane tetracarboxylic acid di Anhydride, cyclopentanetetracarboxylic dianhydride, pyromellitic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, 2,2 ′, 3,3′-benzophenonetetracarboxylic Acid dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 2,2-bis (3,4) -Dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride Bis (3,4-dicarboxyphenyl) sulfone dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, Bis (3,4-dicarboxyphenyl) methane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 2 , 2-bis (2,3-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 1,3-bis [(3,4-dicarboxy) benzoyl] benzene Dianhydride, 1,4-bis [(3,4-dicarboxy) benzoyl] benzene dianhydride, 2,2-bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} propane Anhydride, 2,2-bis {4 [3- (1,2-dicarboxy) phenoxy] phenyl} propane dianhydride, bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} ketone dianhydride, bis {4- [3 -(1,2-dicarboxy) phenoxy] phenyl} ketone dianhydride, 4,4'-bis [4- (1,2-dicarboxy) phenoxy] biphenyl dianhydride, 4,4'-bis [3 -(1,2-dicarboxy) phenoxy] biphenyl dianhydride, bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} ketone dianhydride, bis {4- [3- (1, 2-dicarboxy) phenoxy] phenyl} ketone dianhydride, bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} sulfone dianhydride, bis {4- [3- (1,2- Dicarboxy) phenoxy] Phenyl} sulfone dianhydride, bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} sulfide dianhydride, bis {4- [3- (1,2-dicarboxy) phenoxy] phenyl} Sulfide dianhydride, 2,2-bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} -1,1,1,3,3,3-hexaflupropane dianhydride, 2, 2-bis {4- [3- (1,2-dicarboxy) phenoxy] phenyl} -1,1,1,3,3,3-propane dianhydride, 2,3,6,7-naphthalenetetracarboxylic Acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic acid Anhydride, 3,4,9,10-perylenetate Dianhydride, 2,3,6,7-anthracene tetracarboxylic dianhydride, 1,2,7,8-phenanthrene tetracarboxylic acid dianhydride, and the like. These may be used alone or in combination of two or more.

  In the production of the polyamic acid and the polyimide resin, a terminal sealing agent can be used as necessary. Typical end capping agents are monoamines or dicarboxylic anhydrides.

  Examples of monoamines include aniline, o-toluidine, m-toluidine, p-toluidine, 2,3-xylidine, 2,4-xylidine, 2,5-xylidine, 2,6-xylidine, 3,4-xylidine, 3,5-xylidine, o-chloroaniline, m-chloroaniline, p-chloroaniline, o-bromoaniline, m-bromoaniline, p-bromoaniline, o-nitroaniline, m-nitroaniline, p-nitroaniline O-anisidine, m-anisidine, p-anisidine, o-phenetidine, m-phenetidine, p-phenetidine, o-aminophenol, m-aminophenol, p-aminophenol, o-aminobenzaldehyde, m-aminobenzaldehyde, p-aminobenzaldehyde, o-aminobenzonitrile, m Aminobenzonitrile, p-aminobenzonitrile, 2-aminobiphenyl, 3-aminobiphenyl, 4-aminobiphenyl, 2-aminophenylphenyl ether, 3-aminophenylphenyl ether, 4-aminophenylphenyl ether, 2-aminobenzophenone 3-aminobenzophenone, 4-aminobenzophenone, 2-aminophenylphenyl sulfide, 3-aminophenylphenyl sulfide, 4-aminophenylphenyl sulfide, 2-aminophenylphenylsulfone, 3-aminophenylphenylsulfone, 4-aminophenyl Phenylsulfone, α-naphthylamine, β-naphthylamine, 1-amino-2-naphthol, 2-amino-1-naphthol, 4-amino-1-naphthol, 5-amino-1-naphth 5-amino-2-naphthol, 7-amino-2-naphthol, 8-amino-1-naphthol, 8-amino-2-naphthol, 1-aminoanthracene, 2-aminoanthracene, 9-aminoanthracene, Methylamine, dimethylamine, ethylamine, diethylamine, propylamine, dipropylamine, isopropylamine, diisopropylamine, butylamine, dibutylamine, isobutylamine, diisobutylamine, pentylamine, dipentylamine, benzylamine, cyclopropylamine, cyclobutylamine, Examples include cyclopentylamine and cyclohexylamine.

  Examples of the dicarboxylic acid anhydride include phthalic anhydride, 2,3-benzophenone dicarboxylic acid anhydride, 3,4-benzophenone dicarboxylic acid anhydride, 2,3-dicarboxyphenyl ether anhydride, 3,4-dicarboxyl Phenylphenyl ether anhydride, 2,3-biphenyl dicarboxylic acid anhydride, 3,4-biphenyl dicarboxylic acid anhydride, 2,3-dicarboxyphenyl phenyl sulfone anhydride, 3,4-dicarboxyphenyl phenyl sulfone anhydride, 2,3-dicarboxyphenyl phenyl sulfide anhydride, 3,4-dicarboxyphenyl phenyl sulfide anhydride, 1,2-naphthalenedicarboxylic anhydride, 2,3-naphthalenedicarboxylic anhydride, 1,8-naphthalenedicarboxylic Acid anhydride, 1,2-anthracene dicarboxylic acid Objects, 2,3-anthracene dicarboxylic acid anhydride, 1,9-anthracene dicarboxylic acid anhydride and the like. These monoamines or dicarboxylic anhydrides may be partially substituted with groups that are not reactive with amines or dicarboxylic anhydrides.

  In the production of the polyamic acid, the reaction is preferably performed in an organic solvent. Although the solvent used in reaction is not necessarily limited, For example, the following (a)-(e) etc. can be mentioned.

  (A) phenolic solvent, phenol, o-chlorophenol, m-chlorophenol, p-chlorophenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, 3,5-xylenol.

  (B) N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazo, which are aprotic amide solvents Lydinone, N-methylcaprolactam, hexamethylphosphorotriamide.

  (C) ether solvents 1,2-dimethoxyethane, bis (2-methoxyethyl) ether, 1,2-bis (2-methoxyethoxy) ethane, tetrahydrofuran, bis [2- (2-methoxyethoxy) Ethyl] ether, 1,4-dioxane.

  (D) Amine solvents such as pyridine, quinoline, isoquinoline, α-picoline, β-picoline, γ-picoline, isophorone, piperidine, 2,4-lutidine, 2,6-lutidine, trimethylamine, triethylamine, tripropylamine , Tributylamine.

  (E) Other solvents such as dimethyl sulfoxide, dimethyl sulfone, diphenyl ether, sulfolane, diphenyl sulfone, tetramethyl urea, anisole and the like.

  These solvents may be used alone or in combination of two or more. Among these solvents, N, N-dimethylformamide, N, N-dimethylacetamide, and N-methyl-2-pyrrolidone are particularly preferable.

  A known catalyst can be used in combination in the production of the polyamic acid. For example, as the base catalyst, various amine solvents described in the above (d), organic bases such as imidazole, N, N-dimethylaniline, N, N-diethylaniline, potassium hydroxide, sodium hydroxide, potassium carbonate And inorganic bases represented by sodium carbonate, potassium hydrogen carbonate and sodium hydrogen carbonate. Examples of the acid catalyst include crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methylbenzoic acid, oxybenzoic acid, terephthalic acid, benzenesulfonic acid, p-toluenesulfonic acid, and naphthalenesulfonic acid. It is done.

  In the production of the polyamic acid, the concentration of the polyamic acid in the polyamic acid solution (hereinafter referred to as polymerization concentration) is not particularly limited. A preferable polymerization concentration is 5 to 40% by mass, and more preferably 10 to 30% by mass.

  In the production of the polyamic acid solution, the reaction temperature, reaction time, and reaction pressure are not particularly limited, and known conditions can be applied. That is, the reaction temperature is preferably in the range of −10 to 100 ° C. as an approximate range, but more preferably in the range of around the ice cooling temperature to around 60 ° C., and is most preferably practically 50 to 60 ° C. It is. Moreover, although reaction time changes with kinds of monomer to be used, the kind of solvent, and reaction temperature, 1-48 hours are preferable. More preferably, it is around 2 to 3 hours to around 10 and several hours, and most preferably 4 to 10 hours in terms of implementation. The reaction pressure is sufficient at normal pressure.

  In the present invention, the logarithmic viscosity of the polyamic acid and the polyimide resin is not particularly limited, but the logarithmic viscosity is preferably 0.1 to 2.0, more preferably 0.2 to 1.9, 0.3-1.8 is still more preferable.

A conventionally known method can be used for the production of the carbon film of the present invention (up to the stage before the treatment for adsorbing acetic acid molecules or citric acid molecules ). That is, first, for example, polyamic acid, which is a precursor of a polyimide resin having the above-described structure, is dissolved in an appropriate organic solvent such as N, N-dimethylacetamide, applied to a porous substrate, and then applied. The solution is heated and dried to form a polyimide layer obtained from polyamic acid on the surface of the porous substrate. The application may be repeated a plurality of times as necessary so as to obtain a predetermined film thickness. Conversion from polyamic acid to polyimide is usually carried out by heating at 50 to 400 ° C. A preferred imidization temperature is 100 to 300 ° C.

  Preferred examples of the material for the porous substrate that serves as a support for the carbon film include alumina, silica, cordierite, and the like. The porosity of the porous substrate is preferably about 25 to 55% from the viewpoint of the strength and permeability of the substrate. Moreover, it is preferable that the average pore diameter of a porous base material shall be about 0.005-5 micrometers. The thickness of the porous substrate may be selected as long as it satisfies the strength required for the support and does not impair the permeability of the separation component, and the shape is appropriately selected according to the purpose of use of the carbon membrane. be able to.

  After the application to the porous substrate is completed, the applied solution is heated and dried, the solvent is evaporated by heat treatment, and the polyamic acid is converted to polyimide to form a polyimide layer that is a precursor of the carbon film. . This is carbonized by pyrolysis in a temperature range of about 400 to 1000 ° C. in an oxygen inert atmosphere such as a nitrogen atmosphere to obtain the carbon film of the present invention.

  The film thickness of the carbon film finally obtained is preferably 0.1 to 10 μm, and more preferably 0.1 to 3 μm. If the film thickness of the carbon film is less than 0.1 μm, it is difficult to obtain a sufficient selectivity because the carbon film is insufficiently formed, and if it exceeds 10 μm, the film thickness increases and the permeation flow rate decreases.

  In the production of the carbon film of the present invention, before forming the precursor on the surface of the porous substrate (for example, before applying the polyamic acid which is a polyimide resin precursor), the formation surface (application surface) It is preferable to perform a base treatment for applying an epoxy resin to the surface of the porous base material. By performing such a ground treatment, the permeation flow rate can be improved without impairing the liquid separation performance.

  This is presumably because the base treatment reduces the intrusion into the porous base material such as a polyimide resin as a carbon source of the carbon film, and the carbon film is formed on the surface of the base material. That is, when the base treatment as described above is not performed, since a part of the polyimide resin or the like penetrates into the porous substrate and carbonizes, the liquid that has permeated the carbon film on the porous substrate surface further It must pass through the part of the carbon membrane that has entered the base material where the effective membrane area is reduced, which increases the resistance and lowers the permeation flow rate. On the other hand, when the above-described ground treatment is performed, the liquid that has permeated the carbon film on the surface of the porous base material diffuses into the pores in the base material where the effective membrane area is reduced. Becomes smaller and the permeation flow rate is improved.

The carbon film obtained by carbonizing the precursor is immersed in an aqueous acetic acid solution or an aqueous citric acid solution for 1 to 24 hours at least once after carbonization, and subjected to a treatment for adsorbing acetic acid molecules or citric acid molecules to the pore walls. Thus, the carbon film of the present invention is obtained. As shown in the results of Examples described later, the carbon membrane is not only excellent in acid resistance but also has a characteristic that separation performance is improved by adsorbing acetic acid molecules or citric acid molecules on the pore walls. Therefore, it is possible to obtain a further excellent separation performance by using after performing the above-mentioned treatment in advance.

The reason why the separation performance of the carbon membrane is improved by the treatment is considered to be because the hydrophilicity of the pore walls is improved by adsorbing acetic acid molecules or citric acid molecules to the pore walls. Specific methods for adsorbing acetic acid molecules or citric acid molecules on the pore walls of the carbon film include a method of immersing the carbon film in an acetic acid aqueous solution or a citric acid aqueous solution for 1 to 24 hours. The acetic acid aqueous solution or citric acid aqueous solution to be used is preferably an acetic acid aqueous solution or a citric acid aqueous solution having a pH of 1 to 6. The temperature of the aqueous acetic acid solution or aqueous citric acid solution is preferably 20 to 90 ° C.

  In the separation method of the present invention, the type of the organic solvent to be separated from water is not limited, but when used for separation of water and ethanol, high separation performance can be obtained, so water and ethanol obtained from biomass are used. It is suitable for separation of water and ethanol when recovering ethanol from the contained liquid mixture.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples.

(Production method of carbon film laminate)
Polyamic acid (AURUM (trade name) manufactured by Mitsui Chemicals, Inc.), which is a polyimide precursor represented by the following structural formula (5), is diluted with N, N-dimethylacetamide, and the polyamic acid content is 10 A polyamic acid solution (I) having a mass% was obtained. An alumina porous substrate (manufactured by NGK Co., Ltd., a tube having an average pore diameter of 0.1 μm, a diameter of 12 mm, and a length of 40 mm) is suspended from the polyamic acid solution (I) at a constant speed and immersed, and then again at a constant speed. The polyamic acid was applied by pulling up at a temperature of 90 ° C. for 30 minutes and at 300 ° C. for 1 hour to form a porous substrate and a polyimide resin layer formed on the porous substrate. A provided polyimide resin layer-provided substrate was obtained. The obtained polyimide resin layer-arranged substrate was heat-treated at 700 ° C. to 800 ° C. for 6 hours in a nitrogen atmosphere box furnace to carbonize the polyimide resin layer that is the precursor of the carbon film, and the film thickness was 1 A carbon film laminate of ˜2 μm was obtained. In this heat treatment, the temperature increase rate from room temperature to 300 ° C. is 300 ° C./hour, the temperature increase rate from 300 ° C. to the carbonization temperature (700 ° C. to 800 ° C.) is 60 ° C./hour, from the carbonization temperature to room temperature. The temperature lowering rate was set to 100 ° C./hour.

(Evaluation method of water / ethanol separation performance)
The water / ethanol separation performance (separation coefficient (α) and permeation flow rate (Flux)) of the carbon membrane in this example was evaluated by the pervaporation apparatus shown in FIG. One end of a tube-shaped carbon film (carbon film laminate) 1 is bonded to a glass tube 2 having the same diameter, and the other end is bonded to a dense alumina plate 3 so as to maintain an airtight state. . The carbon film 1 was immersed in a beaker 6 containing a supply liquid 5 made of a water / ethanol mixed liquid kept at a constant temperature by a thermostat 4, and fixed to the beaker 6 together with a thermometer 12 with a silicone stopper 7. The cooling trap 8 was immersed in liquid nitrogen 9 (−196 ° C.), and the supply side pressure of the separation liquid was set to atmospheric pressure, and the permeation side pressure was set to 0.01 Torr by the vacuum pump 14. A PFA tube 10 was used for the permeation path. In the beaker 6, a stirrer 11 for stirring the supply liquid 5 was disposed, and a cooling pipe 13 was attached to the top of the beaker 6. After the elapse of a predetermined time from the start of evaluation, the solid composed of the permeate deposited on the cooling trap 8 was dissolved, and the permeation flow rate (Flux [kg / h · m ² ]) was determined from the mass. Further, the permeate was introduced into a TCD gas chromatograph, and the concentration of the permeate was determined.

(Calculation of separation performance)
As an index of the separation performance of the carbon membrane, water / ethanol separation coefficient α (water / ethanol) represented by the following formula (I) and permeation flow rate (Flux [kg / h ····) represented by the following formula (II) m ² ]). The separation factor is defined as the ratio of the permeate side liquid composition ratio to the supply side liquid composition ratio. In the following mathematical formula (I), Perm (water) and Perm (ethanol) are the volume concentration [vol%] of water and ethanol that permeate the membrane, respectively. Moreover, Feed (water) and Feed (ethanol) are the volume concentration [vol%] of the water and ethanol of a supply liquid, respectively.

α (water / ethanol) = (Perm (water) / Perm (ethanol)) / (Feed (water) / Feed (ethanol)) (I)

Flux = Q / (A · t) (II)
(In formula (II), Q: mass of permeate [kg], A: carbon membrane area [m ² ], t: time [h])

(Comparative Example 1)
The carbon film (carbon film laminate) obtained by setting the carbonization temperature to 700 ° C. in the production method was evaluated by the evaluation method. The water / ethanol ratio of the feed liquid was 90/10 (vol%), the temperature of the feed liquid was 70 ° C., and the water / ethanol separation performance of the carbon membrane was evaluated. As a result, the separation factor α (water / ethanol) = 10, permeation The flow rate Flux was 5 [kg / h · m ² ].

(Comparative Example 2)
After Comparative Example 1, the carbon membrane was washed with ion-exchanged water and dried in the air at 80 ° C. After sufficiently drying, the water / ethanol ratio of the feed liquid was 10/90 (vol%), the temperature of the feed liquid was 25 ° C., and the water / ethanol separation performance of the carbon membrane was evaluated. As a result, the separation factor α (water / ethanol ) = 50, permeation flow rate Flux = 0.15 [kg / h · m ² ].

Example 1
After Comparative Example 2, the carbon membrane was washed with ion-exchanged water and dried in the air at 80 ° C. After sufficiently drying, the carbon film was immersed in an aqueous acetic acid solution having pH = 3 at 75 ° C. for 5 hours. Thereafter, the carbon membrane was taken out from the acetic acid aqueous solution, washed with ion-exchanged water, and dried in the air at 80 ° C. After sufficiently drying, the water / ethanol ratio of the feed liquid was 90/10 (vol%), the temperature of the feed liquid was 70 ° C., and the water / ethanol separation performance of the carbon membrane was evaluated. As a result, the separation factor α (water / ethanol ) = 70 and permeation flow rate Flux = 5 [kg / h · m ² ].

(Example 2)
After Example 1, the carbon membrane was washed with ion-exchanged water and dried in the air at 80 ° C. After sufficiently drying, the water / ethanol ratio of the feed liquid was 10/90 (vol%), the temperature of the feed liquid was 25 ° C., and the water / ethanol separation performance of the carbon membrane was evaluated. As a result, the separation factor α (water / ethanol ) = 280 and permeation flow rate Flux = 0.18 [kg / h · m ² ].

(Example 3)
After Example 2, the carbon membrane was washed with ion-exchanged water and dried in the air at 80 ° C. After sufficiently drying, the carbon film was immersed in an aqueous acetic acid solution having a pH of 1 at 75 ° C. for 5 hours. Thereafter, the carbon membrane was taken out from the acetic acid aqueous solution, washed with ion-exchanged water, and dried in the air at 80 ° C. After sufficiently drying, the water / ethanol ratio of the feed liquid was 90/10 (vol%), the temperature of the feed liquid was 70 ° C., and the water / ethanol separation performance of the carbon membrane was evaluated. As a result, the separation factor α (water / ethanol ) = 70 and permeation flow rate Flux = 4.5 [kg / h · m ² ].

Example 4
After Example 3, the carbon membrane was washed with ion-exchanged water and dried in the air at 80 ° C. After sufficiently drying, the water / ethanol ratio of the feed liquid was 10/90 (vol%), the temperature of the feed liquid was 25 ° C., and the water / ethanol separation performance of the carbon membrane was evaluated. As a result, the separation factor α (water / ethanol ) = 320, and the permeation flow rate Flux = 0.18 [kg / h · m ² ].

(Example 5)
After Example 4, the carbon membrane was washed with ion-exchanged water and dried in the air at 80 ° C. After sufficiently drying, acetic acid having a purity of 99.7% or more was added to the supply liquid to make the water / ethanol / acetic acid ratio 10.0 / 89.8 / 0.2 (vol%), and acetic acid was mixed in the supply liquid. The separation performance in case (acetic acid 2 g / L) was evaluated. As a result of evaluating the water / ethanol separation performance of the carbon membrane at a feed liquid temperature of 25 ° C., the separation factor α (water / ethanol) = 330 and the permeation flow rate Flux = 0.15 [kg / h · m ² ]. It was.

(Example 6)
After Example 5, the carbon membrane was washed with ion-exchanged water and dried in the air at 80 ° C. After sufficiently drying, acetic acid with a purity of 99.7% or more was added to the feed solution to make a water / ethanol / acetic acid ratio of 10.0 / 88.6 / 1.4 (vol%), and acetic acid was mixed in the feed solution. The separation performance in the case (acetic acid 15 g / L) was evaluated. As a result of evaluating the water / ethanol separation performance of the carbon membrane at a feed liquid temperature of 25 ° C., the separation factor α (water / ethanol) = 300 and the permeation flow rate Flux = 0.12 [kg / h · m ² ]. It was.

(Comparative Example 3)
The carbon film (carbon film laminate) obtained by setting the carbonization temperature to 800 ° C. in the production method was evaluated by the evaluation method. The water / ethanol ratio of the feed liquid was 90/10 (vol%), the temperature of the feed liquid was 70 ° C., and the water / ethanol separation performance of the carbon membrane was evaluated. As a result, the separation factor α (water / ethanol) = 47, permeation The flow rate Flux was 0.70 [kg / h · m ² ].

( Reference example )
After Comparative Example 3, the carbon membrane was washed with ion-exchanged water and dried in the air at 80 ° C. After sufficiently drying, as shown in FIG. 2, an Erlenmeyer flask 16 containing acetic acid 15 having a purity of 99.7% or more was prepared, and the carbon membrane 1 was inserted into the Erlenmeyer flask 16 so as not to touch the acetic acid 15. The carbon film 1 is bonded to a glass tube 2 at one end and a dense alumina plate 3 at the opposite end so as to maintain an airtight state. Fixed to an Erlenmeyer flask 16. In this state, the carbon film 1 was exposed to a gas containing acetic acid molecules for 14 days at room temperature by keeping the airtightness in the Erlenmeyer flask 16. Thereafter, the carbon membrane 1 was taken out from the Erlenmeyer flask 16, washed with ion exchange water, and dried in the air at 80 ° C. After sufficiently drying, the water / ethanol ratio of the feed liquid was 90/10 (vol%), the temperature of the feed liquid was 70 ° C., and the water / ethanol separation performance of the carbon membrane was evaluated. As a result, the separation factor α (water / ethanol ) = 73, permeation flow rate Flux = 1.14 [kg / h · m ² ].

(Comparative Example 4)
The carbon film (carbon film laminate) obtained by setting the carbonization temperature to 750 ° C. in the production method was evaluated by the evaluation method. The water / ethanol ratio of the feed liquid was 90/10 (vol%), the temperature of the feed liquid was 70 ° C., and the water / ethanol separation performance of the carbon membrane was evaluated. As a result, the separation factor α (water / ethanol) = 58, permeation The flow rate Flux was 2.8 [kg / h · m ² ].

(Example 8)
After Comparative Example 4, the carbon membrane was washed with ion-exchanged water and dried in the air at 80 ° C. After sufficiently drying, the carbon film was immersed in an aqueous citric acid solution having a pH of 2.2 at room temperature for 6 hours. Thereafter, the carbon membrane was taken out from the citric acid aqueous solution, washed with ion-exchanged water, and dried in the atmosphere at 80 ° C. After sufficiently drying, the water / ethanol ratio of the feed liquid was 90/10 (vol%), the temperature of the feed liquid was 70 ° C., and the water / ethanol separation performance of the carbon membrane was evaluated. As a result, the separation factor α (water / ethanol ) = 80 and permeation flow rate Flux = 3.1 [kg / h · m ² ].

The evaluation results of Examples , Reference Examples and Comparative Examples are summarized in Tables 1 to 5 below. In Examples and Reference Examples shown in Tables 1 to 4, acetic acid molecules are adsorbed on the carbon film, and in Examples shown in Table 5, citric acid molecules are adsorbed on the carbon film. Table 1 shows a carbon film produced at a carbonization temperature of 700 ° C. as a sample, when the water / ethanol ratio of the supply liquid is 90/10 (vol%) and the temperature of the supply liquid is 70 ° C. (Comparative Example 1, Implementation) The evaluation results of Example 1 and Example 3) are summarized. Table 2 uses a carbon film produced at a carbonization temperature of 700 ° C. as a sample, the water / ethanol ratio of the supply liquid is 10/90 (vol%), and the temperature of the supply liquid is 25 ° C. (Comparative Example 2, Example 2). The evaluation results of Example 4) are summarized. Table 3 summarizes the evaluation results in the case where acetic acid was added to the supply liquid (Examples 5 and 6) using a carbon film produced at a carbonization temperature of 700 ° C. as a sample. Table 4 shows a case where a carbon film produced at a carbonization temperature of 800 ° C. is used as a sample, the water / ethanol ratio of the supply liquid is 90/10 (vol%), and the temperature of the supply liquid is 70 ° C. (Comparative Example 3, Reference Example ). This is a summary of the evaluation results. Table 5 shows a case where a carbon film produced at a carbonization temperature of 750 ° C. is used as a sample, the water / ethanol ratio of the supply liquid is 90/10 (vol%), and the temperature of the supply liquid is 70 ° C. (Comparative Example 4 and Example 8). ) Is a summary of the evaluation results.

From the above results, it can be seen that when the water / ethanol mixed solution is supplied to the carbon membrane, water selectively permeates. Further, even when immersed in a strong acid such as pH = 1, the membrane was not destroyed and the water / ethanol separation performance was not lowered, but rather the separation performance was improved by such acid treatment. In addition, the separation performance hardly changed even when acid was mixed in the feed solution. Furthermore, even when exposed to a gas containing acetic acid molecules that show acidity when made into an aqueous solution, an improvement in separation performance was observed.

  The present invention can be suitably used as a method for separating water and ethanol, for example, when recovering ethanol from a liquid mixture containing water and ethanol obtained from biomass.

In an Example, it is the schematic of the pervaporation apparatus used for evaluation of water / ethanol separation performance. In a reference example , it is the schematic which shows the method of exposing the carbon film to the gas containing the acetic acid molecule | numerator which shows acidity when it was made into aqueous solution.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Carbon film (carbon film laminated body), 2 ... Glass tube, 3 ... Alumina plate, 4 ... Constant temperature bath, 5 ... Supply liquid, 6 ... Beaker, 7 ... Silicone stopper, 8 ... Cooling trap, 9 ... Liquid nitrogen, DESCRIPTION OF SYMBOLS 10 ... Tube, 11 ... Stirrer, 12 ... Thermometer, 13 ... Cooling tube, 14 ... Vacuum pump, 15 ... Acetic acid, 16 ... Erlenmeyer flask

Claims (7)

A carbon film obtained by carbonizing a carbon film precursor composed of a resin layer formed on the surface of a porous substrate by pyrolysis in a temperature range of 400 to 1000 ° C. in an oxygen inert atmosphere. A carbon film that has been subjected to a treatment for adsorbing acetic acid molecules or citric acid molecules to pore walls by dipping in an acetic acid aqueous solution or citric acid aqueous solution at least once after the carbonization for 1 to 24 hours . The precursor of the carbon film is a polyimide resin having a repeating unit represented by the following general formula (1) (wherein X is an aliphatic group having 2 to 27 carbon atoms, a cyclic aliphatic group, or a monocyclic aroma) A tetravalent group selected from the group consisting of an aromatic group, a condensed polycyclic aromatic group, and a non-condensed polycyclic aromatic group in which the aromatic groups are connected to each other directly or by a crosslinking member, Y represents an integer of 5 to 10,000, and Y is represented by the following general formula (2). In the general formula (2), at least one of phenylene groups forming the main chain skeleton is an m-phenylene group, and Z Represents direct connection, —O—, —CO—, —S—, —SO ₂ —, —CH ₂ —, —C (CH ₃ ) ₂ — or —C (CF ₃ ) ₂ —, and m represents 1 to 3 R _1-4 and R ′ _1-4 are —H, —F, —Cl, —Br, —I, —CN, —CH _3. , —CF ₃ , —OCH ₃ , phenyl group, 4-phenylphenyl group, phenoxy group or 4-phenylphenoxy group, and R _1-4 and R ′ _1-4 may be the same or different. And a polyamic acid represented by the following general formula (3) (wherein X and Y represent the same groups as described above) which is a precursor of The carbon film according to claim 1, wherein the carbon film is formed by applying to the surface of a porous substrate, heating and drying.

The carbon film according to claim 2, wherein the polyimide resin is represented by the following structural formula (4).

The carbon film according to claim 2, wherein the polyimide resin is represented by the following structural formula (5).

The carbon film according to any one of claims 1 to 4, wherein the porous substrate has an average pore diameter of 0.005 to 5 µm and a porosity of 25 to 55%. By bringing a liquid mixture containing water and an organic solvent into contact with one side of the carbon film according to any one of claims 1 to 5, and selectively allowing water to permeate through the opposite side of the carbon film. A method for separating water and an organic solvent using a carbon membrane, wherein the water and the organic solvent are separated. The method for separating water from an organic solvent using the carbon membrane according to claim 6, wherein the organic solvent is ethanol.

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